#include <fstream>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

long long A[5000001];
int N,K;
int dq[5000001];
int st, dr = -1;
long long s;

int main()
{
    in >> N >> K;
    for (int i = 1; i <= N; i++)
    {
        in >> A[i];
    }
    for (int i = 1; i <= N; i++)
    {
        if (st <= dr && dq[st] == i - K)
        {
            st++;
        }
        while (st <= dr && A[i] <= A[dq[dr]])
            dr--;
        dq[++dr] = i;
        if (st <= dr && i >= K)
        {
            s += A[dq[st]];
        }
    }
    out << s << '\n' ;
    return 0;
}